KR100628797B1 - Active cathode material comprising the lithium-containing composite oxide - Google Patents

Abstract

General formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ , where 0 ≦ x ≦ 0.05 and −0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, and −0.1 ≦ δ ≦ 0.1 (where 0 ≦ y ≦ 0.2) or −0.24 ≦ δ ≦ 0.24 (where 0.2 <y ≦ 0.4), where M is Ti, By having a composition represented by at least one element selected from the group consisting of Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn], the layered crystal structure is stabilized, and has a high density of high capacity lithium containing excellent charge and discharge reversibility. By providing a composite oxide and using it for the positive electrode, a high capacity nonaqueous secondary battery having excellent durability is realized.

Non-aqueous secondary battery, positive electrode active material

Description

Active cathode material comprising the lithium-containing composite oxide

1 is a diagram showing an X-ray diffraction pattern of a lithium-containing composite oxide synthesized in Example 1 of the present invention.

2 is a diagram showing an X-ray diffraction pattern of a lithium-containing composite oxide synthesized in Example 8 of the present invention.

3 is a diagram showing an X-ray diffraction pattern of a lithium-containing composite oxide synthesized in Example 9 of the present invention.

4 is a diagram showing an X-ray diffraction pattern of a lithium-containing composite oxide synthesized in Comparative Example 4 of the present invention.

5 is a diagram showing an X-ray diffraction pattern of a lithium-containing composite oxide synthesized in Comparative Example 5 of the present invention.

6 is a diagram showing a positive electrode discharge curve of a battery using the lithium-containing composite oxide synthesized in Examples 1, 6, 8, Comparative Example 1 and Comparative Example 2 of the present invention as a positive electrode.

The present invention relates to a lithium-containing composite oxide that can be used for the positive electrode material of a nonaqueous secondary battery, a nonaqueous secondary battery using the same, and a method of manufacturing the same.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, the practical use of electric vehicles, and the like, small size, light weight and high capacity secondary batteries are required. At present, a nonaqueous secondary battery represented by a lithium secondary battery using LiCoO ₂ as a positive electrode and a carbon-based material as a negative electrode is commercialized as a high capacity secondary battery according to this demand. The lithium secondary battery has attracted attention as a power source for portable electronic devices in view of its high energy density, compactness, and weight reduction.

LiCoO _{2, which} is used as a positive electrode material of this lithium secondary battery, is easy to manufacture and easy to handle, and thus is widely used as a preferable active material. However, since LiCoO ₂ is manufactured from Co, which is a rare metal, as a raw material, resource shortage is expected to become serious in the future. Moreover, since the price of cobalt itself is high and price fluctuations are large, development of the anode material which is stable in supply at low cost is desired.

For this reason, as the lithium secondary battery positive electrode material in place of LiCoO _2, a lithium manganese oxide-based material is promising. Among them, spinel-type lithium manganese oxides Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ , LiMn ₂ O _4, and the like have been noted, in particular, LiMn ₂ O ₄ is charged to Li in the voltage region near 4V. Since discharge is possible, research is vigorously performed (Japanese Patent Laid-Open Publication No. 6-76824, Japanese Patent Laid-Open Publication No. 7-73883, Japanese Patent Laid-Open Publication No. 7-230802, Japanese Patent Laid-Open Publication No. 7-245106). Publications, etc.).
In addition, using a compound having a very wide composition range as a cathode material of a nonaqueous secondary battery is also disclosed in Japanese Patent Nos. 3064655, 9-199127, 10-69910, and 2000-294242. And the like.

By the way, although LiCoO _{2 has} a theoretical discharge capacity of 274 mAh / g, since a large charge and discharge causes LiCoO ₂ to cause a phase change and affect the cycle life, the practical discharge capacity of the actual lithium secondary battery is 125. It becomes the range which is -140mAh / g.

In contrast, although the theoretical discharge capacity of LiMn ₂ O ₄ is 148 mAh / g, this LiMn ₂ O ₄ also causes a phase change during charge and discharge similarly to LiCoO _2, and when carbon-based materials are used for the negative electrode active material, Since the irreversible capacity of the system material is large, the discharge capacity that can be used when the battery is actually used decreases to about 90 to 105 mAh / g. As is apparent from this, when LiMn ₂ O ₄ is used as the positive electrode active material, the battery capacity cannot be made larger than when LiCoO ₂ is used as the positive electrode active material.

In addition, while the true density of LiCoO ₂ is 4.9 to 5.1 g / cm 3, the true density of LiMn ₂ O ₄ is 4.0 to 4.2 g / cm 3, which is a considerably low value. It becomes more disadvantage in.

In addition, in a lithium secondary battery using LiMn ₂ O ₄ as a positive electrode active material, LiMn ₂ O ₄ itself structure during charging and discharging is unstable, so that the cycle characteristics are worse than that of LiCoO ₂ based batteries.

To solve this problem, LiMn ₂ O ₄ is also different from that review is performed to a layered lithium-manganese oxide of LiMnO ₂ or the like having a different structure as a cathode material. However, the present inventors have conducted detailed studies on the oxide, and as a result, the structure thereof is determined by the composition of the compound, in particular, the presence or absence of elements constituting the oxide other than Li and Mn, the type and amount thereof, and the process until the oxide is formed. It was found that physical properties such as properties and properties were remarkably changed.

For example, when the composition of the spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) fluctuates, and the average valence of Mn approaches trivalent, deformation occurs in the crystal structure of the oxide, and the tetragonal crystal is removed from the cubic spinel structure. Phase changes to form LiMnO ₂ . Since the phase change from the cubic crystal to the tetragonal occurs with charge and discharge in the potential region near 3V with respect to lithium, the same usage as that of the lithium secondary battery charged and discharged at a voltage near 4V should not be used.

In the case where the constituent molar ratio (Li / Mn) of Li and Mn is 1, the crystal structure of LiMnO ₂ exhibits a tetragonal system because of the Jahn-Teller effect due to trivalent Mn.

This compound (LiMnO ₂ ) can be charged and discharged electrochemically in a Li ratio of 0 to 1.0, and theoretically has a discharge capacity of about 285 mAh / g. However, as the tetravalent Mn ratio increases at the time of initial charge, since the phase transition occurs in the spinel structure, the initial charge and discharge curves and the second and subsequent charge and discharge curves not only show different shapes, but also at voltages of 3.5 V or more. The discharge capacity at the end of discharge is significantly reduced from the theoretical value. In addition, since the structural change accompanying the movement of Mn occurs during charge and discharge, there are problems such as poor cycle durability and inability to perform rapid charge and discharge.

Therefore, in order to put practical use of layered lithium manganese oxides such as LiMnO ₂ , it has been necessary to solve the problems of stabilizing the crystal structure, increasing the capacity by improving the reversibility in charge and discharge, and durability in the charge and discharge cycle.

The present invention is made as a result of repeated studies to solve the above-mentioned conventional problems, the structure is stable, excellent charge and discharge reversibility and durability for the charge and discharge cycle, a lithium-containing composite oxide with a high energy density per volume cathode active material The present invention provides a positive electrode and a nonaqueous secondary battery using the positive electrode active material.

That is, the first positive electrode active material provided by the present invention is a positive electrode active material containing a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1 -x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is Ti, Cr, Fe, At least one element selected from the group consisting of Co, Cu, Zn, Al, Ge, and Sn, and y has a composition represented by 0 <y ≦ 0.4.
1) when y is 0 <y≤0.2, δ is -0.1≤δ≤0.1,
2) when y is 0.2 <y≤0.4, at least Co is included as the element M, and δ is -0.24≤δ≤0.24,
The average valence of Mn of the lithium-containing composite oxide is 3.3 to tetravalent.

In addition, the second positive electrode active material provided by the present invention is a positive electrode active material containing a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1). -x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is Ti, Cr, Fe, At least one element selected from the group consisting of Co, Cu, Zn, Al, Ge, and Sn, and y is 0 ≦ y ≦ 0.4.
1) when y is 0≤y≤0.2, δ is -0.1≤δ≤0.1,
2) when y is 0.2 <y≤0.4, at least Co is included as the element M, and δ is -0.24≤δ≤0.24,
The active material different from the lithium-containing composite oxide is characterized by further comprising a lithium-containing cobalt oxide.

The third positive electrode active material provided by the present invention is a positive electrode active material containing a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1). -x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is Ti, Cr, Fe, It is selected from the group which consists of Co, Cu, Zn, Al, Ge, and Sn, and is at least 1 type of element containing Co, y and delta are 0 <y <0.4, -0.1 <= delta <= 0.1, respectively. In the X-ray diffraction measurement using CuKα rays having a composition represented by], the integration intensity of the (003) diffraction peak at which the diffraction angle 2θ is around 18 ° and the (104) diffraction peak at around 44 °, respectively, is I. _{At 18} and I ₄₄ ,
1) When y is 0 <y≤0.2, the cumulative intensity ratio I ₄₄ / I ₁₈ is 0.9 <I ₄₄ / I ₁₈ ≤1.2,
2) When y is 0.2 <y≤0.4, the cumulative intensity ratio I ₄₄ / I ₁₈ is 0.7 ≦ I ₄₄ / I ₁₈ ≦ 1.
The present invention also provides a positive electrode and a nonaqueous secondary battery including the positive electrode active material.

EXAMPLE

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated more concretely by embodiment of this invention. The lithium-containing composite oxide contained in the cathode active material of the present invention is a lithium-containing composite oxide having a layered crystal structure, and is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1- xy-δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, 0 ≦ _y ≦ 0.4, −0.1 ≦ δ ≦ 0.1, and M is Ti, Cr, Fe, At least one element selected from the group consisting of Co, Cu, Zn, Al, Ge, and Sn], containing at least Ni and Mn as constituent elements, and focusing on a composition in which the ratio of Ni and Mn is 1: 1. It is a complex oxide of the extremely limited composition range.

In the present invention, only the limited composition range as described above is selected as the lithium-containing composite oxide for the following reasons. That is, in the lithium manganese oxide, as described above, when the ratio of trivalent Mn increases, a problem arises in that the crystal structure is deformed due to the Yaan-Teller effect and the potential of charge and discharge decreases. For this reason, the Mn valence needs to be set to a value close to tetravalent. However, as the ratio of tetravalent Mn increases, phase transition also occurs easily in the spinel structure, and therefore, stabilization of the crystal structure is necessary.

The inventors have hadeonga by containing Li in LiMnO ₂ with respect to the above-mentioned problems with excessive increase the average valence of Mn, LiMnO, for which the Mn of _2, can be stably constituting the layered lithium-containing complex oxide element, for example Co or Ni It was assumed that the substitution was effective, and the like, and the amount ratio of Li, the type of substitution element and the amount ratio thereof, and the conditions for synthesizing the lithium-containing composite oxide were examined in detail.

As a result, based on the composition represented by the general formula of LiNi _1/2 Mn _1/2 O ₂ where the ratio of Ni and Mn is 1/2: 1/2, that is, 1: 1, Ni and Mn are each x / Mn. 2 is replaced with Li, and the ratio of Ni and Mn is shifted from 1/2: 1/2 by δ / 2 and -δ / 2, respectively, and the ratio of Li is as wide as α, and Ni and Mn are respectively composition substituted by y / 2, where M is at least one element selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn, that is, the general formula Li _{1+ x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ , where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≤ 0.4, -0.1 ≤ δ ≤ 0.1, and M is one or more elements selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn; Under the following conditions, the layered crystal structure is stabilized and excellent in charge / discharge reversibility in the potential region near 4V and durability against charge / discharge cycles. The lithium-containing complex oxide was found to be obtained.
In particular, it was found that when y> 0, that is, when at least one element containing Co is added as the element M, a lithium-containing composite oxide having more excellent characteristics is obtained.

This is because the average valence of Mn in the lithium-containing composite oxide assumes a value near tetravalent (approximately 3.3 to tetravalent), thereby suppressing Mn movement in the crystal during doping and dedoping of Li during charge and discharge. This is considered to be due to the stabilization of the crystal structure.
In addition, in this invention, the value measured by X-ray absorption spectroscopy (XAS) was used as Mn valence.

As described above, X-ray diffraction using CuKα rays for lithium-containing composite oxides having a layered structure stably and excellent in charge / discharge reversibility and excellent durability against charge / discharge cycles, as a component. When the measurement is performed, one diffraction peak corresponding to the (003) and (104) diffraction peaks of LiNiO ₂ exists in the diffraction angle 2θ around 18 ° and around 44 °, respectively, and in the range of 63 ° to 66 °. It can be seen that the diffraction pattern is a single phase complex oxide having the same characteristics as LiNiO ₂ , such as two diffraction peaks corresponding to the (108) and (110) diffraction peaks.

Further, as a result of examining the diffraction pattern in detail, when the area of the diffraction peaks near 18 ° and 44 °, that is, the integration intensity is set to I ₁₈ and I ₄₄ , respectively, the ratio I ₄₄ / I ₁₈ is 0.9 <I ₄₄ / I ₁₈ ≤ 1.2 (where 0≤y≤0.2), or 0.7≤I ₄₄ / I ₁₈ ≤1 (where 0.2 <y≤0.4), and 63 ° to The difference θa of the diffraction angles 2θ of two diffraction peaks in the range of 66 ° is 0.3 ° ≦ θa ≦ 0.6 ° (where 0 ≦ y ≦ 0.2), or 0.55 ° ≦ θa ≦ 0.75 ° ( However, it can be seen that it has a characteristic (when 0.2 <y ≤ 0.4).

Likewise, with such a lithium-containing LiMn ₂ O ₄ the charge and discharge curve of a composite oxide having a spinel structure, as can be charged and discharged in a voltage region in the vicinity of 4V, it is used as a replacement for a conventional positive electrode active material LiCoO ₂ It becomes possible.

In addition, it was found that the lithium-containing composite oxide having the above composition had a high density of 4.55 to 4.95 g / cm 3, and became a material having a high volumetric energy density. Since the true density of the lithium-containing complex oxide containing Mn in a predetermined range can vary substantially depending on the composition, but the structure is stabilized in a narrow composition range, a single phase is likely to form, close to the true density of LiCoO ₂ It is assumed to be a large value. In particular, when the composition is close to the stoichiometric ratio, it becomes a large value, and it is found that at -0.015 ≦ x + α ≦ 0.015, it becomes a high density composite oxide of about 4.7 g / cm 3 or more.

As described above, the lithium-containing composite oxide of the present invention is based on a composition in which Ni and Mn are 1: 1, such as LiNi _1/2 Mn _1/2 O ₂ , but the composition is examined in detail again. Bar, in the vicinity of the composition where the ratio of Ni, Mn and M is 1: 1: 1, that is, represented by the general formula LiNi _1/3 Mn _1/3 M _1/3 O ₂ , and y = _1/3 , It turned out that the lithium containing composite oxide which has especially outstanding characteristic is obtained.

General Formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ [wherein M is Ti, Cr, Fe, Co, Cu, In the case of at least one element selected from the group consisting of Zn, Al, Ge, and Sn), the deviation (δ / 2) of the ratio between Ni and Mn is only small, but is determined in a composition range of 0.2 <y≤0.4. Since the stability of the structure is higher and a single phase is more likely to be formed, the deviation of the ratio between Ni and Mn may be increased. For this reason, in the above general formula, the range taken by δ when 0 ≦ y ≦ 0.2 is narrow to −0.1 ≦ δ ≦ 0.1, whereas when 0.2 <y ≦ 0.4, the range of δ is −0.1 ≦ δ ≦ 0.1 In addition, it is possible to be widened to -0.24≤δ≤0.24.

Moreover, since the true density becomes larger than the compound of the composition range of 0 <= y <= 0.2 in the composition range of 0.2 <y <= 0.4, it also became clear that it was a material suitable for higher capacity | capacitance. That is, in the composition range of 0.2 <y≤0.4 in the compound of stoichiometric composition, the true density is about 4.75-4.95g / cm <3>, The true density in the composition range of 0 <y <= 0.2 is about 4.55 ~ 4.74 g / cm 3.

Here, the upper limit of y is 0.4, where the composition of y> 0.4, that is, when the amount of substitution in element M is more than 0.4, abnormalities that impair the stability of the compound are easily formed in the target complex oxide. For losing.

By the way, the lithium-containing composite oxide is quite difficult to obtain the single phase simply by mixing and firing a Li compound, a Mn compound, a Ni compound and the like.

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Since the diffusion rate in solids such as Ni and Mn is low, it is difficult to uniformly diffuse them in the synthesis reaction, and it is presumed that the reason is that the elements are not uniformly distributed in the produced oxide.

Therefore, the inventors of the present invention have also studied in detail the method for synthesizing the oxide, and as a result, by firing a composite compound containing at least Ni and Mn as constituent elements and a Li compound, the single phase of the lithium-containing composite oxide of the present invention is fired. The knowledge that can be synthesized relatively easily was obtained. That is, composite compounds of constituent elements such as Ni and Mn are synthesized in advance, and by firing them together with Li compounds, the metal elements are uniformly distributed in the oxide formation reaction, thereby facilitating single phase formation. Of course, the method of synthesizing the lithium-containing composite oxide of the present invention is not limited to the above method, but the physical properties of the resulting composite oxide, ie, structural stability, charge / discharge reversibility, and true density, are greatly increased depending on which synthetic process is passed. It is estimated to change.

Here, as a composite compound containing at least Ni and Mn as a constituent element, for example, a coprecipitation compound containing at least Ni and Mn, a hydrothermally synthesized compound, a mechanically synthesized compound, a compound obtained by heat-treating them, etc. You can use An oxide or hydroxide of Ni and Mn can be preferably used, such as Ni _0.5 Mn _0.5 (OH) ₂ , NiMn ₂ O ₄ , Ni _0.5 Mn _0.5 OOH. In addition, when synthesizing a lithium-containing composite oxide containing M (M is at least one element selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn) as a constituent element, at least Ni And the desired oxide can be obtained by mixing and baking a composite compound containing Mn, a Li compound, and a compound containing M, but if possible, it is preferable to use a composite compound containing Ni and Mn and M from the beginning. Do. Moreover, what is necessary is just to select suitably the ratio of Ni, Mn, and M in the said composite compound according to the composition of the lithium containing composite oxide made into the objective.

In addition, various lithium salts may be used as the Li compound, and examples thereof include lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, and lithium lactate. And lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide, and the like, and among these, lithium hydroxide monohydrate in that no gas adversely affects the environment such as carbon dioxide, nitrogen oxides and sulfur oxides. Is most preferably used.

The composite compound containing at least Ni and Mn as constituent elements and the Li compound are mixed at a ratio almost in accordance with the composition of the desired lithium-containing composite oxide, and the mixture is, for example, in an atmosphere containing oxygen. By baking at about 700 to 1100 degreeC for 1 to 24 hours, the lithium containing composite oxide of this invention can be synthesize | combined.

As the heat treatment in the calcination, the temperature is heated to a temperature lower than the calcination temperature (approximately 250 to 850 ° C.), rather than being heated up to a predetermined temperature at a time, preheating is performed by holding at that temperature, and the temperature is raised to the calcination temperature to react It is preferable to proceed. In the process of producing the lithium-containing composite oxide of the present invention, the reaction between the Li compound and the composite compound containing at least Ni and Mn as components occurs in stages, and finally, the lithium-containing composite oxide is produced via the intermediate product. This is because it is estimated. In other words, when the temperature is raised to the firing temperature in a short time, the Li compound and the composite compound containing at least Ni and Mn as constituent elements partially react to the final stage, and the lithium-containing composite oxide produced thereby interferes with the reaction of the unreacted material. The problem that the uniformity of a composition is impaired may arise. Moreover, in order to shorten the time required for the reaction step and to obtain a homogeneous lithium-containing composite oxide, it is effective to perform heating stepwise. Although this preheating time in particular is not restrict | limited, Usually, what is necessary is just to carry out about 0.5 to 30 hours.

In the step of calcining the mixture of the Li compound and the complex compound containing at least Ni and Mn as constituent elements, the dry mixed mixture may be used as it is, but the mixture is dispersed in a solvent such as ethanol to form a slurry, It is preferable to mix about 30 to 60 minutes in a ball mill or the like, and to use the dried material to further increase the homogeneity of the lithium-containing composite oxide to be synthesized.

The atmosphere of the heat treatment may be performed in an atmosphere containing oxygen, that is, in air, in a mixed atmosphere of inert gas such as argon, helium, nitrogen, and oxygen gas, or in oxygen gas. It is preferable to make oxygen ratio in atmosphere into 10% or more by volume ratio.

As said gas flow rate, it is preferable to set it as 1 dm <3> / min or more per 100g of said mixtures, and 1-5 dm <3> / min is more preferable. When the gas flow rate is small, that is, when the gas flow rate is low, the reaction proceeds unevenly, and impurities such as Mn ₂ O ₃ and Li ₂ MnO ₃ are easily generated.

By using the lithium-containing composite oxide of the present invention obtained by the method described above as a positive electrode active material, a nonaqueous secondary battery is produced as follows, for example.

If necessary for the lithium-containing composite oxide, the positive electrode mixture used by mixing conductive additives such as scale graphite and acetylene black with a binder such as polytetrafluoroethylene and polyvinylidene fluoride is used as it is, or It is applied to or impregnated with a base which also serves as a whole, and is used in combination with the base. As the substrate, for example, a metal network such as aluminum, stainless steel, titanium, copper, punching metal, expanded metal, foam metal, metal foil, or the like can be used.

In addition, although only the said lithium containing composite oxide may be used as a positive electrode active material, other active materials other than the said lithium containing composite oxide may be included, It can be mixed with another active material, or can be used as a composite with another active material. For example, the lithium-containing composite oxide is less likely to have electronic conductivity compared to lithium-containing cobalt oxide such as LiCoO _2, and thus, a problem that large voltage discharge or voltage drop at the end of discharge tends to occur. However, by mixing and using lithium containing cobalt oxide excellent in electronic conductivity, the said voltage drop can be suppressed and a discharge characteristic can be improved. As this lithium-containing cobalt oxide, compounds other than LiCoO ₂ may be used, such as LiCo _1-t Ni _t O ₂ , in which a part of Co is substituted with another element, for example, Ni. In this case, when the proportion of the lithium-containing cobalt oxide is too large, durability such as high temperature storage characteristics tends to decrease, but the proportion of the lithium-containing cobalt oxide is set to 50% or less of the entire active material in terms of mass ratio. It is possible to prevent the deterioration of the high temperature storage characteristics.

As the negative electrode active material facing the positive electrode, lithium or a lithium-containing compound is usually used, but as the lithium-containing compound, a lithium alloy such as a Li-Al alloy, a Li-Pb alloy, a Li-In alloy, or a Li-Ga alloy And an element capable of forming an alloy with lithium, such as Si, Sn, and Mg-Si alloys, or an alloy containing these elements as a main agent. Moreover, carbonaceous materials, such as graphite, fibrous carbon, lithium containing composite nitride, etc. can be used other than oxide type materials, such as Sn oxide and Si oxide. Moreover, you may use what compounded the said many material. Composites of carbonaceous materials and Si are also preferably used. In addition, also in the case of cathode production, the same method as that of the said anode can be used.

Although the ratio of the active material in the positive electrode and the negative electrode varies depending on the type of the negative electrode active material, in general, the lithium-containing composite is obtained by setting (mass of the positive electrode active material) / (mass of the negative electrode active material) = 1.5 to 3.5. The characteristics of the oxide can be used well. However, in the case of using a composite material with other components such as an element capable of forming an alloy with lithium, an alloy containing these elements as a main body, a lithium-containing composite nitride, or a carbonaceous material as the negative electrode active material, Since the capacity of the negative electrode becomes too large in the ratio, it is preferable to set (mass of the positive electrode active material) / (mass of the negative electrode active material) = 4 to 7.

As the nonaqueous electrolyte in the nonaqueous secondary battery of the present invention, an organic solvent-based liquid electrolyte in which an electrolyte is dissolved in an organic solvent, that is, an electrolyte or a polymer electrolyte in which the electrolyte is held in a polymer can be used. Although the organic solvent contained in this electrolyte solution or a polymer electrolyte is not specifically limited, It is preferable to contain chain ester from a load characteristic point. As such a linear ester, organic solvents, such as linear carbonate represented by dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, ethyl acetate, methyl propionate, are mentioned, for example. These chain esters may be used alone or in combination of two or more thereof. Particularly, in order to improve low temperature properties, the chain esters preferably occupy at least 50% by volume in the total organic solvent, and in particular, the chain esters may be used as the total organic solvent. It is more preferable to occupy 65 volume% or more in the inside.

However, as an organic solvent, in order to improve the discharge capacity, it is preferable to mix and use the ester with high induction rate (induction ratio: 30 or more) in order to improve the discharge capacity. As a specific example of such ester, cyclic ester is preferable, For example, cyclic carbonate represented by ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, (gamma) -butyrolactone, ethylene glycol sulfide, etc. are mentioned. These are mentioned, Especially cyclic carbonates, such as ethylene carbonate and a propylene carbonate, are more preferable.

It is preferable that such a high dielectric constant ester contain at least 10% by volume, in particular at least 20% by volume, of the total organic solvent. Moreover, 40 volume% or less is preferable at the point of a load characteristic, and 30 volume% or less is more preferable.

Moreover, as a solvent which can be used together other than the said high dielectric constant ester, 1, 2- dimethoxyethane, 1, 3- dioxolane, tetrahydrofuran, 2-methyl- tetrahydrofuran, diethyl ether, etc. are mentioned, for example. have. In addition, an amineimide organic solvent, a sulfur containing or a fluorine-containing organic solvent can also be used.

As a soluble solubility in an organic solvent, for example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ ( SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCnF _{2n + 1} SO ₃ (n ≧ 2) and the like are used alone or in combination of two or more thereof. Especially, LiPF ₆ , LiC ₄ F ₉ SO _3, etc. which can obtain favorable charge / discharge characteristics are used preferably. Although the electrolyte concentration in electrolyte solution is not specifically limited, 0.3-1.7 mol / dm <3>, especially about 0.4-1.5 mol / dm <3> is preferable.

Moreover, in order to improve the stability and storage characteristic of a battery, you may contain an aromatic compound in a nonaqueous electrolyte. As an aromatic compound, benzene, biphenyl, or fluorobenzene which have alkyl groups, such as cyclohexylbenzene and tert- butylbenzene, is used preferably.

It is good that the separator has sufficient strength and can hold a large amount of electrolyte solution. In view of such a separator, a polyolefin microporous film or nonwoven fabric, such as polypropylene, polyethylene, copolymer of propylene and ethylene, has a thickness of 5 to 50 µm. Etc. are preferably used. In particular, in the case of using a thin separator with a thickness of 5 to 20 µm, battery characteristics tend to deteriorate during charge and discharge cycles, high temperature storage, and the like. However, the lithium-containing composite oxide of the present invention is excellent in stability. The battery can be functioned stably.

Next, examples of the present invention will be described. However, this invention is not limited only to these Examples.

<Example 1>

Ammonia water adjusted to pH of about 12 was prepared by adding sodium hydroxide into the reaction vessel, and while stirring it vigorously, a mixed aqueous solution containing 1 mol / dm 3 of nickel sulfate and manganese nitrate, respectively, and 25 mass% ammonia water Is added dropwise using a metering pump at a rate of 46 cm 3 / min and 3.3 cm 3 / min to produce co-precipitation compounds of Ni and Mn, respectively. At this time, the reaction solution temperature was maintained at 50 ° C, and the dropwise addition of an aqueous sodium hydroxide solution at a concentration of 3.2 mol / dm 3 was simultaneously performed so that the reaction solution pH was maintained at about 12. At the time of reaction, the reaction was carried out while purging nitrogen gas at a rate of 1 dm 3 / min so that the reaction liquid atmosphere became an inert atmosphere.

The resulting product was washed with water, filtered and dried to form a hydroxide containing Ni and Mn in a ratio of 1: 1. 0.2 mol of this hydroxide and 0.198 mol of LiOH.H ₂ O were weighed, and the mixture was dispersed with ethanol. After the slurry was in shape, the mixture was mixed with a planetary ball mill for 40 minutes and dried at room temperature to prepare a mixture. Subsequently, the mixture is placed in a crucible made of alumina, heated to 800 ° C. in an air stream of 1 dm 3 / min, preheated by holding at that temperature for 2 hours, and again heated to 1000 ° C. and calcined for 12 hours. Composite oxides were synthesized. The prepared compound was ground in a mortar and preserved in a desiccator as powder.

With respect to the powder of the oxide, the composition was measured by an atomic absorption spectrometer, and it was found that the composition was represented by Li _0.99 Ni _0.5 Mn _0.5 O ₂ . In addition, Mn X-ray absorption spectroscopy (XAS) is performed using BL4 beamport of superconducting small emission light source "Aurora" (Sumitomo Electric Co., Ltd.) of Ritsumeikan University SR Center. It was. The obtained data analysis was based on the Journal of the Electrochemical Society, 146 p2799-2809 (1999), and was performed using analysis software "REX" (manufactured by Rigaku Electric Co., Ltd.). In addition, in order to determine the Mn valence of the compound, MnO ₂ and LiNi _0.5 Mn _1.5 O ₄ (both standard samples as compounds having Mn having an average valence of 4) as standard samples, and LiMn ₂ O ₄ (average valence values) Standard Samples as Compounds with Mn at 3.5 Val), LiMnO ₂ and Mn ₂ O ₃ (Standard Samples as Compounds with Mn at Average Valence) and MnO (Standard Samples as Compounds with Mn at Average Valence) ) Was used. A regression line showing the relationship between the K absorption end position of Mn and the Mn valence of each standard sample was obtained, and the K absorption end position of Mn of the compound was almost the same as the K absorption end position of MnO ₂ and LiNi _0.5 Mn _1.5 O ₄ . From the above, the average valence of Mn of the compound was determined to be tetravalent.

Since Ni could not obtain a proper compound as a standard sample having trivalent or higher Ni as Ni, NiO and LiNi _0.5 Mn _1.5 O ₄ , which are compounds having Ni with an average valence, Since the K absorption end positions were almost the same, the average valence of Ni of the compound was determined to be divalent.

<Example 2>

0.198 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.202 mol of LiOH.H ₂ O were weighed and then Li _1.01 Ni _0.495 Mn _0.495 O was prepared in the same manner as in Example 1. _The lithium containing composite oxide represented by ₂ was synthesize | combined.

<Example 3>

0.196 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.204 mol of LiOH.H ₂ O were weighed, and in the same manner as in Example 1 below, Li _1.02 Ni _0.49 Mn _0.49 O _The lithium containing composite oxide represented by ₂ was synthesize | combined.

<Example 4>

0.194 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.206 mol of LiOH.H ₂ O were weighed and then Li _1.03 Ni _0.485 Mn _0.485 O was _{prepared in the} same manner as in Example 1. _The lithium containing composite oxide represented by ₂ was synthesize | combined.

Example 5

0.192 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.208 mol of LiOH.H ₂ O were weighed and then Li _1.04 Ni _0.48 Mn _0.48 O in the same manner as in Example 1 below. _The lithium containing composite oxide represented by ₂ was synthesize | combined.

<Example 6>

0.19 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.21 mol of LiOH.H ₂ O were weighed, and in the same manner as in Example 1, Li _1.05 Ni _0.475 Mn _0.475 O _The lithium containing composite oxide represented by ₂ was synthesize | combined.

<Example 7>

Ni, Mn, and Ni were mixed in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate at 0.9 mol / dm 3, 0.9 mol / dm 3, and 0.2 mol / dm 3, respectively, was added dropwise. The hydroxide containing Co in 4.5: 4.5: 1 ratio was obtained. In the same manner as in Example 1 below, a lithium-containing composite oxide represented by Li _0.99 Ni _0.45 Mn _0.45 Co _0.1 O ₂ was synthesized.

<Example 8>

Li _0.99 Ni _0.375 Mn in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate in a ratio of 0.75 mol / dm 3, 0.75 mol / dm 3, and 0.5 mol / dm 3, respectively, was added dropwise. A lithium-containing composite oxide represented by _0.375 Co _0.25 O ₂ was synthesized.

Example 9

Li _0.99 Ni _0.34 Mn in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate in a ratio of 0.67 mol / dm 3, 0.66 mol / dm 3, and 0.66 mol / dm 3, respectively, was added dropwise. A lithium-containing composite oxide represented by _0.33 Co _0.33 O ₂ was synthesized.

<Example 10>

Li _0.99 Ni _0.3 Mn in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate in a ratio of 0.6 mol / dm 3, 0.6 mol / dm 3, and 0.8 mol / dm 3, respectively, was added dropwise. A lithium-containing composite oxide represented by _0.3 Co _0.4 O ₂ was synthesized.

Comparative Example 1

0.2 mol of LiOH.H ₂ O and 0.2 mol of MnOOH are weighed and mixed in a planetary ball mill for 30 minutes to prepare a mixture, which is then calcined at 450 ° C. for 10 hours in a 1 m 3 / min nitrogen stream, A tetragonal lithium manganese oxide represented by LiMnO ₂ was synthesized.

Comparative Example 2

0.18 mol of hydroxide containing Ni and Mn synthesized in the same manner as in Example 1 and 0.22 mol of LiOH.H ₂ O were weighed, and in the same manner as in Example 1 below, Li _1.1 Ni _0.45 Mn _0.45 A lithium-containing composite oxide represented by O ₂ was synthesized.

Comparative Example 3

Li _0.99 Ni _0.25 Mn _{0.25 in the} same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate in a ratio of 0.5 mol / dm 3, 0.5 mol / dm 3, and 1 mol / dm 3, respectively, was added dropwise. A lithium-containing composite oxide represented by Co _0.5 O ₂ was synthesized.

<Comparative Example 4>

Li _0.99 Ni _0.2 Mn in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate, manganese nitrate, and cobalt sulfate at 0.4 mol / dm 3, 0.4 mol / dm 3, and 1.2 mol / dm 3, respectively, was added dropwise. A lithium-containing composite oxide represented by _0.2 Co _0.6 O ₂ was synthesized.

Comparative Example 5

A lithium-containing composite oxide represented by Li _0.99 Ni _0.25 Mn _0.75 O ₂ in the same manner as in Example 1 except that a mixed aqueous solution containing nickel sulfate and manganese nitrate was respectively added at a rate of 0.5 mol / dm 3 and 1.5 mol / dm ₃ . Was synthesized.

Comparative Example 6

Lithium-containing represented by Li _0.99 Ni _0.6 Mn _0.3 Co _0.1 O ₂ in the same manner as in Example 7 except that the ratio of nickel sulfate and manganese nitrate in Example 7 was set to 1.2 mol / dm 3 and 0.6 mol / dm 3, respectively. Composite oxides were synthesized. That is, the lithium-containing composite oxide of Comparative Example 6 is different from Example 7 only in the ratio of Ni and Mn.

<Reference Example>

0.2 mol of LiOHH ₂ O, 0.1 mol of Ni (OH) ₂ and 0.1 mol of MnOOH are weighed and mixed in a planetary ball mill for 30 minutes to obtain a mixture, which is placed in alumina crucible and air at 800 ° C. for 10 hours to firing, to synthesize the lithium-containing complex oxide represented by the composition of LiNi _0.5 Mn _0.5 O _2.

Table 1 shows a list of each of the lithium-containing composite oxides of the above Examples 1 to 10, Comparative Examples 1 to 6, and Reference Examples.

TABLE 1

The X-ray diffraction measurement by CuKα ray was performed about the lithium-containing composite oxides of Examples 1 to 10, Comparative Examples 1 to 6, and Reference Examples of the present invention.

Although the lithium-containing composite oxides of Examples 1 to 10, Comparative Examples 2 to 6, and Reference Examples of the present invention exhibited an X-ray diffraction pattern similar to LiNiO ₂ having a layered structure, the X-ray diffraction patterns of Comparative Examples 3 to 5 and Reference Examples The peak which shows the generation | occurrence | production of the above was also confirmed. In addition, the X-ray diffraction pattern of Comparative Example 1 was a tetragonal pattern different from LiNiO ₂ . In Examples 1 to 10, Comparative Example 2, and Comparative Example 6 of the present invention, peaks resulting from the above generation were not found, that is, the diffraction peaks at which the diffraction angle 2θ is around 18 ° and around 44 ° It was confirmed that the oxide obtained was a single phase of a lithium-containing composite oxide having a structure similar to LiNiO _{2 because} each had one and two diffraction peaks existing in the range of 63 ° to 66 °. In addition, although diffraction peaks existing within the range of 63 ° to 66 ° were found to be adjacent to the peak by the Kα ₁ line of Cu, the peak by the Kα ₂ line was also confirmed. As a diffraction peak to be considered, only the peak by the above Kα ₁ line is considered.

Among the above, the X-ray diffraction patterns of Example 1, Example 8, Example 9, Comparative Example 4, and Comparative Example 5 were illustrated as Figs.

In addition, the ratio (I ₄₄ / I ₁₈ ) of the integration intensity I ₁₈ and I ₄₄ of the diffraction peaks near 18 ° and around 44 ° and the diffraction angle difference between the two diffraction peaks existing in the range of 63 ° to 66 ° ( The value measured about (theta) a) is shown in Table 2. In addition, the lithium containing composite oxide of the comparative example 1 differs in crystal structure from the thing of this invention, and in the lithium containing composite oxide of the comparative examples 3-5 and the reference example, three pieces exist in the range which is 63 degrees-66 degrees by the above generation. Since the above diffraction peaks existed, Table 2 does not describe the data of these compounds.

TABLE 2

In the lithium-containing composite oxides of Examples 1 to 7 in which 0 ≦ y ≦ 0.2, the integrated intensity ratio I ₄₄ / I ₁₈ is in the range of 0.9 to 1.2, and the diffraction angle difference θa is in the range of 0.3 ° to 0.6 °. Was in. Further, in the 0.2 <y≤0.4 in the Example 8~10 I ₄₄ / I ₁₈ is 0.7 to 1 range, θa was in a range of 0.55 ° ~0.75 °. On the other hand, in Comparative Example 2 and Comparative Example 6 whose composition is out of the range of the present invention, either one of I ₄₄ / I ₁₈ or θa deviates from the above range, and in Comparative Examples 3 to 5 and Reference Example, as described above, Three or more diffraction peaks existed in the range of 63 ° to 66 °.

Next, about the lithium containing composite oxide of Examples 1-10, Comparative Examples 1-6, and a reference example of this invention, the true density was measured using the true density measuring apparatus. The results are shown in Table 3. In addition, the measurement error was at most ± 0.03 g / cm 3.

TABLE 3

In the lithium-containing composite oxides of Examples 1 to 10 of the present invention, the true density is 4.57 to 4.82 g / cm 3, and in particular, Examples 1 and 2 having a nearly stoichiometric composition, that is, -0.015 <x + α ≦ 0.015 And Examples 7 to 10, the true density became a large value of 4.7 g / cm 3 or more. In particular, in Examples 8 to 10 in which the substitution amount y in the element M was 0.2 <y≤0.4, the largest value of 4.76 g / cm 3 or more was obtained.

On the other hand, Comparative Example 1, which is a conventional tetragonal composite oxide, or Comparative Example 2, in which the composition is largely deviated from the stoichiometric composition, have a small value of 4.5 g / cm 3 or less, and the Ni and Mn ratios are outside the scope of the present invention. In Example 5 and Comparative Example 6, despite the almost stoichiometric composition, the true density was lower than that in Examples 1, 2 and 7 to 10 of the present invention. In addition, since the homogeneity was inferior due to the above-mentioned generation or the remaining of the unreacted substance, the lithium-containing composite oxide of the reference example also had a lower true density than the lithium-containing composite oxide of Example 1.

Here, the true density of the lithium-containing composite oxides of Comparative Example 3 and Comparative Example 4 is higher than that of the examples of the present invention, but this is because LiCoO ₂ having a true density of about 5.1 g / cm 3 or more is produced as above. As a matter of fact, the composite oxide of the true density shown in Table 3 was not obtained.

Next, the discharge capacity of the lithium-containing composite oxides of Examples 1 to 10 and Comparative Examples 1 and 2 of the present invention was measured by the method shown below.

To 20 parts by mass of polyvinylidene fluoride as a binder, 250 parts by mass of N-methyl-2-pyrrolidone was added and heated to 60 ° C to dissolve polyvinylidene fluoride in N-methyl-2-pyrrolidone. And binder solution were prepared. 450 mass parts of said lithium containing complex oxides were added to this binder solution as a positive electrode active material, 5 mass parts of carbon black and 25 mass parts of graphite were added as a conductive support agent, and it stirred, and prepared the slurry-like coating material. This coating material was uniformly coated on both sides of an aluminum foil having a thickness of 20 µm, dried, and then press-molded with a roller press, followed by cutting to produce a strip-shaped anode having an average thickness of 190 µm and a width of 483 mm and a length of 54 mm.

A separator made of a microporous polyethylene film having a thickness of 25 μm is disposed between the electrodes using a positive electrode prepared as described above and a negative electrode made of lithium foil, and a volume ratio of ethylene carbonate and ethyl methyl carbonate is 1: 3 mixed. A nonaqueous solution in which LiPF ₆ was dissolved in a solvent at a concentration of 1.0 mol / dm 3 was used as an electrolyte, and a reference electrode of lithium was placed to assemble a battery for evaluating the discharge capacity of the positive electrode.

The battery was charged to 4.3 V with a current density of 0.2 mA / cm 2 for the area of the positive electrode, and discharged to 3.1 V at the same current density to measure the discharge capacity. The measured discharge capacity is shown in Table 4 as values converted per unit mass (mAh / g) and per unit volume (mAh / cm 3) of the positive electrode active material. In addition, the positive electrode discharge curve of the battery using the lithium containing composite oxide of Example 1, Example 6, Example 8, Comparative Example 1, and Comparative Example 2 is shown in FIG.

TABLE 4

The lithium-containing composite oxides of Examples 1 to 10 of the present invention were capable of operating at a high discharge potential of 3.5 V or more and exhibited a large discharge capacity at 136 to 153 mAh / g, but in Comparative Examples 1 and 2, 130 mAh / g or less In addition, since the lithium-containing composite oxide of the present invention had a higher true density, the difference became more remarkable in terms of the discharge capacity per unit volume.

Moreover, in order to evaluate the characteristic as the nonaqueous secondary battery of the said lithium containing composite oxide, the nonaqueous secondary battery was produced with the following structures.

<Example 11>

A nonaqueous secondary battery was fabricated using the lithium-containing composite oxides of Example 1 and Example 9 alone as positive electrode active materials. The positive electrode was obtained by applying a paste prepared by mixing 92 parts by mass of a positive electrode active material, 4.5 parts by mass of artificial graphite, 0.5 parts by mass of carbon black, and 3 parts by mass of polyvinylidene fluoride onto an aluminum foil base material, followed by pressure molding after drying. .

The negative electrode was obtained by applying a paste prepared by mixing 92 parts by mass of natural graphite, 3 parts by mass of low crystalline carbon, and 5 parts by mass of polyvinylidene fluoride on a copper foil base material, followed by pressure molding after drying.

The positive electrode and the negative electrode were surrounded by a separator made of a microporous polyethylene film having a thickness of 16 μm, and LiPF ₆ was 1.2 mol / dm 3 in a mixed solvent having a volume ratio of 1: 2 of ethylene carbonate and ethyl methyl carbonate as an electrolyte. Using the dissolved material, a cylindrical nonaqueous secondary battery having a capacity of 600 mAh was produced. In addition, the mass ratio [(mass of positive electrode active material) / (mass of negative electrode active material)] of the positive electrode active material and the negative electrode active material was 1.9.

<Example 12>

A nonaqueous secondary battery was produced in the same manner as in Example 11, except that 70 mass% of the lithium-containing composite oxide of Example 1 and 30 mass% of LiCoO ₂ were mixed and used as the positive electrode active material.

Comparative Example 7

As the positive electrode active material, nonaqueous 2 was prepared in the same manner as in Example 11 except that LiCoO ₂ and LiNi _0.8 Co _0.2 O ₂ used in the lithium-containing composite oxide of Comparative Example 6 and a commercially available nonaqueous secondary battery were used alone. A secondary battery was produced.

The cycle characteristics and the high temperature storage characteristics of the nonaqueous secondary batteries of Example 11, Example 12, and Comparative Example 7 were evaluated. The cycle characteristics were evaluated by the discharge capacity ratio (capacity retention rate (%)) after 100 cycles to the discharge capacity at the beginning of the cycle when charging and discharging was performed at a current value of 1 C (600 mA). The high temperature storage characteristics are compared with the changes in the discharge capacity before and after the storage when the storage test is performed for 20 days at 60 ° C, that is, the discharge capacity when the battery is charged and discharged at a current value of 1 C, before and after storage. It evaluated by the discharge capacity ratio (capacity retention (%)) after storage with respect to the previous discharge capacity. Table 5 shows the results of these property evaluations.

<Table 5>

Although the nonaqueous secondary batteries of Examples 11 and 12, which used the lithium-containing composite oxide of the present invention as the positive electrode active material, had excellent cycle characteristics and high temperature storage characteristics despite the use of a thin separator having a thickness of 16 µm, The nonaqueous secondary battery of Comparative Example 6, which uses only LiCoO ₂ or LiNi _0.8 Co _0.2 O ₂ as a cathode active material, which is used in Comparative Example 6 or a commercially available nonaqueous secondary battery having a composition outside the scope of the invention, has cycle characteristics and high temperature storage characteristics. It is inferior to that of the present invention. That is, by using the lithium composite oxide of the present invention together with a conventional active material as the cathode active material, it was possible to improve the cycle characteristics and the high temperature storage property of the nonaqueous secondary battery.

In addition, when the batteries of Example 11 and Example 12 were discharged at 2C (1200 mA) and the characteristics of the large current discharge were examined, the discharge capacity of the battery of Example 11 was 525 mAh, whereas the battery of Example 12 was 573 mAh. Significant improvement in furnace characteristics was confirmed. This is by mixing lithium containing cobalt oxide with the lithium containing composite oxide of this invention.

Example 13

As a negative electrode active material, a nonaqueous secondary battery was produced using a material obtained by complexing Si and a carbonaceous material. Si powder and artificial graphite were mixed in a planetary ball mill and compounded, and the obtained composite was sieved to obtain a negative electrode active material. As the positive electrode active material, a lithium-containing composite oxide of Example 1 was used, except that a nonaqueous secondary battery was produced in the same manner as in Example 11. However, the mass ratio of the positive electrode active material to the negative electrode active material was 6.6. In this battery, the mass ratio of the positive electrode active material could be increased by using a high capacity material as the negative electrode active material. Thus, the discharge capacity could be increased by about 7% in the same size as in Example 11.

With regard to the nonaqueous secondary battery, the discharge capacity at 2C discharge was measured, resulting in a battery having 605 mAh and excellent characteristics even at a large current discharge. This is presumably because by increasing the mass ratio of the positive electrode active material, the load on the positive electrode active material at the time of discharge is reduced and the voltage drop is reduced.

As described above, in the present invention, the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _(1-xy-δ ) / 2M _y O ₂ [where 0 ≦ _x ≦ 0.05, -0.05≤x + α≤0.05, 0≤y≤0.4, -0.1≤δ≤0.1 (where 0≤y≤0.2) or -0.24≤δ≤0.24 (where 0.2 <y≤0.4 ), M has a composition represented by at least one element selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn], whereby the stability of the crystal structure is high and the charge and discharge reversibility is good. It is possible to provide a high density lithium-containing composite oxide.

In addition, by using the lithium-containing composite oxide as the positive electrode active material, it is possible to provide a nonaqueous secondary battery having high durability and high capacity. Since the lithium-containing composite oxide is resource-rich and inexpensive Mn is one of the main constituent elements, the lithium-containing composite oxide is suitable for mass production and can contribute to cost reduction.

Claims (32)

A positive electrode active material containing a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn And y and δ each have a composition represented by 0 <y ≦ 0.2 and −0.1 ≦ δ ≦ 0.1], and the average valence of Mn is 3.3 to tetravalent. . The positive electrode active material according to claim 1, wherein a molar ratio of Ni and Mn in the lithium-containing composite oxide is 1: 1. The positive electrode active material according to claim 1 or 2, wherein the lithium-containing composite oxide has a true density of 4.55 to 4.95 g / cm 3. A positive electrode active material containing a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn At least one element containing Co, and y and δ are each represented by 0.2 <y ≦ 0.4 and −0.24 ≦ δ ≦ 0.24, and the average valence of Mn is 3.3 to tetravalent. A positive electrode active material, characterized in that. The positive electrode active material according to claim 4, wherein a molar ratio of Ni, Mn, and element M contained in the lithium-containing composite oxide is 1: 1: 1. The cathode active material according to claim 1, 2, 4 or 5, further comprising another active material different from the lithium-containing composite oxide. The cathode active material according to claim 6, wherein the other active material contains lithium-containing cobalt oxide. The cathode active material according to claim 1, 2, 4 or 5, wherein the average valence of Mn contained in the lithium-containing composite oxide is tetravalent. The positive electrode active material according to claim 1, 2, 4 or 5, wherein the average valence of Ni contained in the lithium-containing composite oxide is divalent. A positive electrode active material comprising a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy- δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge and Sn Selected from at least one element containing Co, y and δ are each 0.2 <y ≤ 0.4, and-0.24 ≤ δ ≤ 0.24; and as an active material different from the lithium-containing composite oxide, A cathode active material further comprising lithium-containing cobalt oxide. The cathode active material according to claim 10, wherein the lithium-containing composite oxide is Li _{1 + α} Ni _1/3 Mn _1/3 CO _1/3 O ₂ , wherein −0.05 ≦ _α ≦ 0.05]. The positive electrode active material according to claim 10 or 11, wherein the proportion of the lithium-containing cobalt oxide is 50% by mass or less of the entire positive electrode active material. The positive electrode containing the positive electrode active material of Claim 1, 2, 4, or 5. The positive electrode containing the positive electrode active material of Claim 6. The positive electrode containing the positive electrode active material of Claim 10 or 11. A positive electrode active material comprising a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy- δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge and Sn At least one element selected, each of y and δ being 0 ≦ y ≦ 0.2, and −0.1 ≦ δ ≦ 0.1], and further comprising a lithium-containing cobalt oxide as an active material different from the lithium-containing composite oxide. A positive electrode active material comprising a. The positive electrode active material according to claim 16, wherein a molar ratio of Ni and Mn in the lithium-containing composite oxide is 1: 1. The positive electrode active material of Claim 16 in which the element M contained in the said lithium containing composite oxide contains Co. The positive electrode containing the positive electrode active material of Claim 16, 17, or 18. A positive electrode active material comprising a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy- δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge and Sn At least one element containing at least Co, and y and δ are each represented by 0 <y ≦ 0.2 and −0.1 ≦ δ ≦ 0.1], and in X-ray diffraction measurement using CuKα rays, When the integrated intensities of the (003) diffraction peaks in which the diffraction angle 2θ is around 18 ° and the (104) diffraction peaks near 44 ° are set to I ₁₈ and I ₄₄ , the ratio thereof is I ₄₄ / I ₁₈ is 0.9 <I ₄₄ / I ₁₈ ≦ 1.2. The positive electrode active material according to claim 20, wherein a molar ratio of Ni and Mn in the lithium-containing composite oxide is 1: 1. The positive electrode active material according to claim 20, further comprising another active material different from the lithium-containing composite oxide. 23. The cathode active material according to claim 22, wherein said other active material contains lithium-containing cobalt oxide. The positive electrode containing the positive electrode active material of Claim 20, 21, 22, or 23. A positive electrode active material comprising a lithium-containing composite oxide having a layered crystal structure, wherein the lithium-containing composite oxide is represented by the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy- δ) / 2} M _y O ₂ [where 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, and M is selected from the group consisting of Ti, Cr, Fe, Co, Cu, Zn, Al, Ge and Sn At least one element containing at least Co, and y and δ are each represented by 0.2 <y ≦ 0.4 and −0.1 ≦ δ ≦ 0.1], and in X-ray diffraction measurement using CuKα rays, When the integrated intensities of the (003) diffraction peaks in which the diffraction angle 2θ is around 18 ° and the (104) diffraction peaks near 44 ° are set to I ₁₈ and I ₄₄ , the ratio thereof is I ₄₄ / I ₁₈ is 0.7 ≦ I ₄₄ / I ₁₈ ≦ 1. The positive electrode active material according to claim 25, wherein the molar ratio of Ni and Mn contained in the lithium-containing composite oxide is 1: 1. 27. The cathode active material according to claim 26, wherein the molar ratio of Ni, Mn, and element M contained in the lithium-containing composite oxide is 1: 1: 1. 27. The cathode active material according to claim 25, further comprising another active material different from the lithium-containing composite oxide. 29. The cathode active material according to claim 28, wherein said other active material contains lithium-containing cobalt oxide. A positive electrode comprising the positive electrode active material according to claim 25, 26, 27, 28, or 29. A nonaqueous secondary battery comprising the positive electrode, the negative electrode and the nonaqueous electrolyte according to claim 24. A nonaqueous secondary battery comprising the positive electrode, the negative electrode, and the nonaqueous electrolyte according to claim 30.

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